Antennas with loop coupled feed system



April 28, 1970 K. G. BALMAIN ANTENNAS WITH LOOPCOUPLED FEED SYSTEM 2Sheets-Sheet 1 Filed June 16, 1967 FIG. 2 PRIOR ART) F G. 7 (PRIOR ART)Attorney April 28, 1970 K. G. BALMAIN 3,509,573

ANTENNAS WITH LOOP COUPLED FEED SYSTEM Filed June 16, 1967 3Sheets-Sheet 2 TO 7 E RMI NA Tl ON A ttorn e y I W /KM United StatesPatent 3,509,573 ANTENNAS WITH LOOP COUPLED FEED SYSTEM Keith GeorgeBalmain, Toronto, Ontario, Canada, as-

signor to The Governors of The University of Toronto, Toronto, Ontario,Canada Filed June 16, 1967, Ser. No. 646,675 Int. Cl. Hfllq 11/10,21/12, 9/16 U.S. Cl. 343-7925 16 Claims ABSTRACT OF THE DISCLOSURE Anantenna array comprising substantially coplanar and parallel unitaryelements arranged in side by side relation and a feed or collectorsystem therefor extending longitudinally of the array comprising a pairof conductors disposed to form in combination loops extending betweenand electrically insulated from adjacent elements; each of the loopsbeing comprised of a portion of each of the conductors extendinglongitudinally of and contiguous each of the respective adjacentelements with the directions of such portions of each conductor beingreversed at adjacent elements and with the direction of such portion ofone conductor being opposite to the direction of such portion of theother conductor at each element when tracing the directions of suchconductors from one end of the array.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to antennas for use in radiatedwave propagation communicationsystems and more particularly, to a novel system for feeding antennasfrom a source in the case of transmission or collecting signals fromantennas in the case of reception resulting in more simplified andmechanically stronger antennas than heretofore possible, wherein theantenna elements or dipoles associated with the feed system are unitaryelements rather than pairs of separate members.

The invention has, for example, particular application to the field ofantennas such as are employed to provide unidirectional radiationpatterns (or to provide unidirectional reception) that are essentiallyindependent of frequency over wide bandwidths. An antenna of the typefor which the invention has particular application is fully described inU.S. Patent 3,210,767, granted Oct. 5, 1965. Su'ch an antenna is knownas a log-periodic antenna and involves the use of an array ofsubstantially coplanar and parallel dipoles or elements ofprogressively, mathematically defined, increasing length and spacing inside by side relationship.

Description of the prior art In the prior art, as represented, forexample, by U.S. Patent 3,210,767, the dipoles or elements areconstituted by pairs of members which are fed in sequence by a commonfeeder which alternates in phase between successive elements or dipoles,the array being symmetrical about a line passing through the midpoint ofeach element or dipole constituted by the two separate members. Such anarray has a backfire radiation being fed fro-m the smaller end andradiating toward the smaller end.

The necessity of forming each element or dipole of a pair of members sothat the feed can be alternated in phase between successive dipolesgives rise to mechanical problems of supporting the elements in theirproper orientation and leads to misalignment of the pair of members ofeach element.

SUMMARY OF THE INVENTION According to the'present invention the elementsor dipoles of the antenna are single or unitary members and the couplingbetween the elements and the feed or collector system therefor isachieved by means of a novel conductor or feed system which is loopcoupled to the elements to provide the required alternating phaserelationship between adjacent elements without requiring the division ofsuch elements into separate members thereby greatly simplifying theantenna structure, while providing important mechanical advantages andeliminating individual element or dipole misalignment.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be betterunderstood from the following detailed description taken in conjunctionwith the accompanying drawing in which:

FIGURE 1 is a schematic view of a prior art log-periodic dipole antennaarray to which the present invention has particular application.

FIGURE 2 is a schematic view of the manner in which an antenna array ofthe type illustrated in FIGURE 1 is fed.

FIGURE 3 is a schematic view of a log-periodic antenna array of theclass of FIGURES 1 and 2 but embodying the present invention.

FIGURE 4 is a perspective view of a log-periodic antenna of the typeschematically illustrated in FIGURE 3 embodying the invention andshowing an optional supporting boom in dotted lines.

FIGURE 5 is an enlarged fragmented perspective view of a modified formof antenna embodying the invention.

FIGURE 6 is a view similar to FIGURE 5 but illustrating a modified formof loop coupled feed system.

FIGURES 7 and 8 illustrate uniform periodic and tapered periodic antennaarrays respectively constructed to embody the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIGURE 1 theantenna array illustrated comprises a plurality of dipoles or elements,1, 2, 3, 4, etc. each formed of two elements lalb, 2412b, 3a3b and4114b, etc., which have a length L L L and L etc., and are separated adistance d d 61 etc., in a mathematical relationship such that where Kis a constant having a value less than I. As shown in FIGURE 2 the arrayis fed at its narrow end from a source 5 by a transmission linecomprised by lines 6 and 7, the lines 6 and 7 being transposed orreversed between adjacent elements or dipoles being connected to theends of the separate members lalb, 2a2b, etc. Such an antenna radiatesin the backfire direction, that is, toward the source 5 and providesunidirectional frequency independent or log-periodic operation.

The portion of such an array which acts as the radiator is centeredaround those elements near resonance, that is, where Ln is approximatelyone-half a wave length, which elements absorb substantially all of theinput power and convert it to a radiated electromagnetic field. As thefrequency changes the portion of the array which serves as the radiatorshifts along the array so that again such portion is centered around theelements whose length is approximately one-half wave length. Because ofthe backfire radiation the larger elements which are not excited do notinterfere with the radiation pattern while the shorter inactiveelements, because of their smaller size and spacing and alternatephasing, do not materially effect the radiation pattern.

For proper operation of the individual members of the dipoles, namely,the members 1a1b, 202b, etc. must be rigidly supported not only inrelation to adjacent dipole elements but to each other giving rise tomechanical support problems.

With reference to FIGURES 3 and 4 there is illustrated a log-periodicantenna having the characteristics of the antenna of FIGURES 1 and 2 butembodying the present invention. In the antennas illustrated in FIGURES3 and 4, it will be seen that the dipoles or elements instead of beingformed of pairs of separate members are single unitary members 11, 12,13, 14, etc. These elements 11, 12, 13, 14 have the same mathematicallydetermined relative length and spacing as described in relation to theelements or dipoles of the array of FIGURE 1.

The feed system for the elements 11, 12, 13 etc. comprises a pair offeed conductors, wires or lines and 16 of suitable conducting material,such as copper, connected to a source 17. It will be understood that inthe case of use of the antenna array for receiving such conductors,wires, or lines 15 and 16 then form collectors and will be connected toa suitable receiver input. The conductors 15 and 16 are insulated frombut form, in effect, loops electromagnetically coupled to the elements11, 12, 13, 14, etc. to excite and provide the appropriate phasereversal between adjoining elements or dipoles as hereinafter more fullydescribed.

As illustrated in FIGURE 4, it will be seen that each of the feed linesor conductors 15 and 16 has a generally square Wave shape the length,and preferably also the amplitude, of the waveform progressivelyincreasing corresponding to the progressive increase in the spacing andlength of the elements 11, 12, 13, 14, etc. and with the waveform of oneline being of opposite hand to the other. Thus, conductor or line 15 isbeing or shaped to provide portions or lengths 18 and 19 extendinggenerally parallel to the axis of the antenna array between adjacentelements and portions or lengths and 21 of appreciable extent extendingsubstantially parallel to and along or immediately contiguous to theantenna elements. The portions 20 and 21 thus provide electromagneticcoupling over their length between the line 15 and the antenna elements11, 12, 13, 14 etc. to provide a relatively tight coupling between theline and the elements with the line to element coupling at adjacentelements being substantially reversed or approximately 180 out of phase.

It will be understood that the coupling between the line portions 20 and21 and the antenna elements will be dependent upon the length of suchportions and their proximity to the elements. In general, for closelyassociated feed line portions 20 and 21 and the respective antennaelements, acceptable coupling can be achieved with the length of suchportions 20 and 21 ranging from about onetwentieth to one-third of thelength of the associated element. Thus, while the length of the lineportions, eg 20 and 21, preferably progressively increase proportionallyto the increase of the length of the antenna elements along the array,they do not necessarily need to do so, as long as the above relationshipobtains.

As a structure, it may be considered that the series of couplingportions 20 and 21 and connecting portions 18 and 19 of line 15 form, ineffect, open sided loops with the open sides facing in oppositedirections when moving from one such loop to the next adjacent loop.

Line or conductor 16 is similarly but oppositely bent or shaped toprovide portions or lengths 23 and 24 corresponding to the lengths 18and 19 of line 15 extending generally parallel to the axis of theantenna array between adjacent antenna elements and portions or lengthsand 26 corresponding to the portions 20 and 21 of line 15 extendingsubstantially parallel to and along or immediately contiguous to theantenna elements. Again the portions 25 and 26 of line 16 provideelectromagnetic coupling over their length between the line 16 and theantenna ele- 4 ments 11, 12, 13, 14 etc. to provide a relatively tightcoupling between the elements and the line with the coupling between theline and adjacent elements again being substantially reversed orapproximately out of phase.

As before, the series of coupling portions 25 and 26 and connectingportions 23 and 24 of line 16 form, in effect, open sided loops with theopen sides facing in opposite directions when moving from one such loopto the next adjacent loop. Between any pair of antenna elements the openside of the respective loop defined by either lengths 18, 19 and 20, orlengths 18, 19 and 21 of line 15 faces the open side of thecorresponding loop formed by either lengths 23, 24 and 25, or lengths23, 24 and 26 of line 16, and the two lines 15 and 16, thus, incombination form, in effect, closed loops to provide a feed or collectorsystem which may be conveniently referred to as a loop coupled feed orcollector system which couples the antenna elements to the source 17 inthe case of transmission or to a suitable receiver input in the case ofreception.

Because at any one antenna element the coupling portion 20 or 21 of line15 extends along the element in the reverse direction to thecorresponding coupling portion 25 or 26 of line 16 when tracing thelines 15 and 16 from one end of the array then the resulting coupling,due to the substantially 180 phase relation of the currents in the twolines will be additive at each such antenna element. While the couplingof the two lines are additive at each element, as above explained, thecoupling is substantially reversed when moving from one element to thenext adjacent element in either direction to provide the requisiteunidirectional backfire field pattern in the case of transmission or torespond to a directional field directed at the small end of the antennaarray in case of reception.

The lines 15 and 16 may conveniently be formed by conductors or wireshaving insulated coatings 27 so that they are electrically insulatedfrom the antenna elements 11, 12, 13, 14 etc. or alternatively, if it isdesired to use bare conductors or wires, it will be understood thatsuitable insulators may be employed between the lines and the antennaelements to preclude direct electrical connection therewith.

The feed lines 16 and 15 may also be shaped to cause the coupling lineportions 20, 21, and 25 and 26 to lie alternately on opposite sides,that is, above and below adjacent elements 11, 12 etc., as shown inFIGURE 4. Alternatively, one line may run on one side of the elementsand the other line may run on the other side of the elements as shown inFIGURE 6.

In such a feed system, as described in relation to FIG- URE 4, it willbe understood that the impedance is substantially constant, independentof frequency, and may be readily matched with the source 5 in the caseof transmission, or the receiver input in case of reception.

The feed lines 16 and 15 may be terminated with an impedance Z whichconveniently may simply be a section of a shorted line.

The lines 16 and 15 may themselves be sufficiently rigid and the singleelements 11, 12, 13 and 14 etc. clamped or otherwise secured by anysuitable means (not shown) to the pairs of line coupling sections 20,25, or 21, 26, to provide a rigid self-supporting antenna array withoutrequiring further support, since only the spacing of the elements needbe maintained.

Alternatively, as a further support, a central boom 31 may be employedas illustrated in dotted line in FIGURE 4 to give added strength andrigidity. Such a boom may be metal and the elements 11, 12, 13, 14 etc.may be secured or clamped directly to such boom by any conventionalmeans.

FIGURE 5 illustrates a modified antenna array in the form of a printedcircuit embodying the invention. In this array the antenna elements 32,33, 34 etc. are printed on a supporting non-conducting sheet 3-5 and thefeed system is comprised by the feed or collector lines 36 and 37 eachof which again is of generally square wave formation to providegenerally axially extending connecting portions or lengths 36a and 36band 37a, 37b, respectively, extending between adjacent elements andcoupling portions or lengths 38a38b, and 39a39b, respectively, whichextend parallel and contiguous to but are insulated from such adjacentelements to provide a close electromagnetic coupling therewith. In theembodiment illustrated in FIGURE 5, each of the feed lines 36 and 37alternates from one side of the sheet 35 to the other between theantenna elements being passed through the sheet at the intermediatepoints 40 with the result that the coupling portions 38a and 38b and 39aand 39b alternately lie on opposite sides of the adjacent antennaelements.

As before, it will be seen that the feed or collector system comprisedby the conductors 36 and 37 provides, in efiect, a series of loops whichare electromagnetically coupled to the elements 32, 33, 34 etc., theopposing directions of the coupling lengths 38a, 39a and 38b, 39b of theconductors 36 and 37 providing additive coupling at each individualantenna element, while the reversal of the directions of the couplinglengths 38a3'8b and 39a39b at adjacent elements provides a substantialreversal in phase between adjacent antenna elements. Thus, thisarrangement gives rise to the unidirectional backfire radiation patternin the case of transmission or renders the array unidirectionallyresponsive to arriving electromagnetic fields over a broad band offrequencies.

FIGURE 6 illustrates an antenna array generally similar to thatillustrated in FIGURE 5, except that one of the feed lines or conductors46 lies on one side of the antenna elements 42, 43, 44 etc. and theother of the feed lines or conductors 47 lies on the other side of theelements. Again the elements 42, 43, 44 may be printed in anon-conducting sheet 45 and the feed conductors may be formed as part ofthe printed circuit or may comprise stampings mounted on the sheet 45the sheet serving to insulate the one feed conductor line 46 from theantenna elements 42, 43, 44 etc. the other line 47 being insulated fromthe said elements by an insulating coating 47 or any other insulatingmeans which may comprise a sheet similar to sheet 45 so that theelements 42, 43 and 44 are sandwiched between two dielectric sheets.

Again the conductors or feed lines 46 and 47 are shaped to provideconnecting portions 48a48b and 49a and 49b, respectively, and couplingportions 50a50b and SlaSlb, respectively, tightly coupled to the antennaelements. Each of the conductors 46 and 47 again thus forms, in eifect,a series of open sided alternately facing loops extending betweenadjacent antenna elements with the open sides of the loops of oneconductor facing the open sides of the loops of the other conductor.Thus the conductors 46 and 47 again, in effect, provide in combinationclosed loops electromagnetically coupled to adjacent elements 42, 43 and44 with the coupling between adjoining elements being substantiallyreversed to provide the desired unidirectional frequency independentantenna characteristics above described.

While the invention has been particularly described in relation to alog-periodic antenna the principle of the invention of antenna elementfeeding or collecting by means of a loop coupled feed or collectingsystem can also be applied advantageously to uniform periodic antennaarrays such as illustrated in FIGURE 7, or tapered periodic antennaarrays as illustrated in FIGURE 8. In each case the elements 52, 53, 54etc. and 62, 63, 64 etc., respectively, can be formed as solid or onepiece elements fed by the feed lines 56 and 57 and 66 and 67,respectively, and the structure may be made rigid with or without booms70 and 71, respectively.

While specific embodiments of the invention have been described, it willbe understood that many variations may be made in antenna arrays and thespecific feed arrangements while still advantageously employing theprinciple of a loop coupled feed system with solid antenna elementswithout departing from the spirit or scope of the invention. Inaddition, it will be understood that while, for simplicity, theinvention has been described and illustrated in relation to simplesingle antenna arrays, the invention is applicable to antenna systemswhich may comprice multiple or complex arrangements of antenna arrays.

I claim:

1. An antenna comprising an array of substantially coplanar and parallelunitary elements arranged in side by side relation and means couplingsaid elements comprising a first conductor extending between saidelements and having a coupling portion at each element of appreciablelength extending parallel and contiguous to such element and insulatedtherefrom, the said portions at adjacent elements extending in oppositedirections when traced from either end of the array, and a secondconductor corresponding to the first conductor but of opposite handhaving a coupling portion at each element of appreciable lengthextending parallel and contiguous to such element and insulatedtherefrom, the said portions-of said second conductor at adjacentelements extending in opposite directions when traced from said arrayend and with the directions of said portions of said first conductorbeing opposite to the directions of said portions of said secondconductor at each element.

2. An antenna as claimed in claim 1 in which said first and secondconductors constitute a feed or collector system extendinglongitudinally of the array and form in combination loops extendingbetween and electrically insulated from adjacent elements.

3. An antenna as claimed in claim 1 in which said elements are ofprogressively changing length and spacing along the array to form alog-periodic antenna array.

4. An antenna as claimed in claim 1 in which said first and secondconductors are rigid and form a support structure for said elements.

5. An antenna as claimed in claim 1 in which at least one of saidelement array and said conductors is formed by a printed circuit on acarrier sheet.

6. An antenna as claimed in claim '1 in which said coupling portions ofsaid first and second conductors extend on opposite sides or adjacentelements of said array.

7. An antenna as claimed in claim 1 in which said coupling portions ofeach of said first and second conductors lies on opposite sides ofadjacent elements of said array with the opposed coupling portions ofsaid first and second conductors at each element lying on opposite sidesof said element.

8. A broad band unidirectional log-periodic antenna comprising an arrayof substantially coplanar and parallel elements of progressivelyincreasing length and spacing characterized in that each of saidelements is a single member and the feed or collector system for saidelements comprises a pair of conductors each of generally square Waveformation having portions extending generally parallel to the axis ofthe array between adjacent elements and coupling portions of appreciablelength extending generally perpendicular to the array axis and paralleland contiguous to and insulated from said elements, the pair ofconductors being of opposite hand with the coupling portions of one ofsaid conductors extending in an opposite direction to the couplingportions of the other of said conductors when traced from an end of saidarray and the coupling portions of each of said conductors extending inopposite directions at adjacent elements when traced from an end of saidarray.

9. A broad band antenna as claimed in claim 8 in which the generallysquare Wave formation of each of said conductors has a progressivelyincreasing amplitude and spacing corresponding to the increasing lengthand spacing of said elements.

10. A broad band antenna as claimed in claim 9 in which said conductorsare rigid and form a support structure for said elements.

11. A broad band antenna as claimed in claim 9 in which said elementsare mounted on a supporting boom extending axially of said elementarray.

12. A broad band antenna as claimed in claim 8 in which at least one ofsaid element array and pair of conductors is formed as a printed circuitdeposited on an insulating sheet.

13. A broad band antenna as claimed in claim 8 in which the couplingportions of one of said pair of conductors extend on one side ofadjacent elements of said array and the coupling portions of the otherof said pair of conductors extend on the side of adjacent elements ofsaid array opposite to the coupling elements of the first mentionedconductor.

14. A broad band antenna as claimed in claim '8 in which said couplingportions of each of said conductors lie alternately on opposite sides ofadjacent elements of said array and the coupling portions of saidconductors at any one element lying on opposite sides thereof.

15. A broad band antenna as claimed in claim 8 in which said conductorsare stampings.

References Cited UNITED STATES PATENTS 2,433,804 12/1947 Wolff 343-811 X2,716,703 8/1955 Kane 343-814 X 3,056,960 10/1962 Wickersham 343-811 X3,300,784 1/1967 Ervine 343-8l2 X HERMAN KARL SAALBACH, Primary ExaminerT. VEZEAU, Assistant Examiner US. Cl. X.R. 3438l4, 822

